How Do I Fix a Running Toilet?

A running toilet is almost never a plumbing emergency, but it is a quiet monthly waste of water and money. The tank works like a small machine: push the handle, the flapper lifts and water flows into the bowl, the tank empties, the flapper drops, and the fill valve refills the tank until the float tells it to stop. When something in that cycle does not seat correctly, water keeps trickling past the flapper or the valve never shuts off, and the toilet runs.

Start by lifting the lid and watching. Flush the toilet and observe: if water keeps leaking into the bowl after the flush, that is the flapper. If water keeps running through the overflow tube into the bowl, that is the fill valve or float. You can also add a few drops of food coloring to the tank and let it sit; if color bleeds into the bowl without flushing, the flapper is leaking. That single test tells you exactly where to start.

Replace the flapper first, because it is a $10 part that solves most running toilets. Flappers are rubber, and over a few years they warp, stiffen, or collect mineral deposits so they no longer seal the flush valve opening. Take the old flapper with you to the hardware store to match the size and shape, or buy a universal kit, and install it by slipping the ears over the overflow tube pins and hooking the chain to the handle with just enough slack to let the flapper sit flat.

A chain that is too tight holds the flapper open and makes the toilet run. A chain with too much slack can flip over the flapper and jam it. Adjust the chain so there is a small amount of play, then flush to confirm a clean, positive seal. While you are in there, wipe mineral buildup off the flush valve seat with a cloth; a rough seat keeps even a new flapper from sealing.

If the toilet has a flush volume adjustment, usually a dial or clip on the fill valve, set it so the tank refills to the mark molded inside the tank, which balances a strong flush against water use. A tank set too high wastes water on every flush; one set low risks weak flushes and double flushing that wastes even more. Older toilets also benefit from a look at the overflow tube: the fill hose should be clipped into the tube so it sends a little water down on each refill for a proper flush, and it should never hang below the water line where a backflow condition can siphon water. If the toilet is original to a 1990s or earlier home and runs no matter what you adjust, the whole tank mechanism may simply be due, and modern toilets use dramatically less water per flush, so the replacement conversation is not the expensive one you might fear.

If water keeps running into the tank, the problem is the fill valve not shutting off. Most fill valves have a float that rises with the water level and shuts the flow when the tank is full. Bend or adjust the float arm slightly so the water stops about an inch below the top of the overflow tube, and check that the water level is not constantly spilling over the overflow tube, which is the classic cause of a toilet that runs silently forever.

If the fill valve itself is worn, often flagged by a hissing or squealing as it runs, replacement kits are inexpensive and come with clear instructions. Shut off the water supply valve behind the toilet, flush to drain the tank, unscrew the old valve, and install the new one at the same height. If the shutoff valve at the wall is stiff or seized, see our guide on shutting off home water to know your backups before you need them.

Most running toilets are a DIY job, but a few symptoms point past the tank. If the toilet continues to run after a new flapper and a new fill valve, or if you hear water running even when you can see both parts seated correctly, the problem may be in the flush valve, the seal at the base of the toilet, or a supply line issue. A toilet that runs and periodically makes a gurgling or sucking sound can signal a venting problem in the drain system, worth bringing in a professional.

The money math matters too: a toilet leaking continuously can waste thousands of gallons a year. If the fix is not obvious within a couple of attempts, an hour of a plumber's time is cheaper than the water bill, and far cheaper than a subfloor repair if the leak is at the base rather than the tank.